An optimal temperature profile for achieving the highest amount of ethylene production in a fixed bed plug flow reactor of oxidative coupling of methane (OCM) was determined and analyzed from chemical reactions point of view. A performance index was defined to solve the problem and the optimal temperature profile was found by means of "piecewise linear continuous optimal control by dynamic programming" (PLCOCIDP) algorithm. The performance obtained from the optimal temperature profile was compared with the best isothermal performance of the reactor, gained from optimization calculations. It was concluded that the quantity of ethylene production by applying the optimal temperature profile is about 42% greater than that of the best isothermal performance of the reactor at 1096.3 K. It was also observed that maximization of ethylene production and minimization of carbon dioxide production are interrelated in this system. The effects of total pressure and initial oxygen concentration were studied as well. The optimal temperature profile spread out and its minimum point rose a little with increasing the concentration of oxygen and/or decreasing the total pressure. Moreover, when the total pressure or initial oxygen mole fraction was elevated, the ethylene molar flux increased, however the selectivity of ethylene reduced in case of increasing the oxygen molar flux. (C) 2007 Elsevier B.V. All rights reserved.